Background: Bone marrow stromal cells (BMSC) have been successfully employed for movement deficit recovery in spinal cord injury (SCI) rat models. One of the unsettled problems in cell transplantation is the relative high proportion of cell death, specifically after neural differentiation. According to our previous studies, p75 receptor, known as the death receptor, is only expressed in BMSC in a time window of 6-12 hours following neural induction. Moreover, we have recently reported a decreased level of apoptosis in p75-suppressed BMSC in vitro. Therefore, our objective in this research was to explore the functional effects of transplanting p75:siRNA expressing BMSC in SCI rats. Methods: Laminectomy was performed at L1 vertebra level to expose spinal cord for contusion using weight-drop method. PBS-treated SCI rats (group one) were used as negative controls, in which cavitations were observed 10 weeks after SCI. pRNA-U6.1/Hygro- (group two, as a mock) and pRNA-U6.1/Hygrop75 shRNA- (group three) transfected BMSC were labeled with a fluorescent dye, CM-DiI, and grafted into the lesion site 7 days after surgery. The Basso-Beattie-Bresnehan locomotor rating scale was performed weekly for 10 weeks. Results: There was a significant difference (P�0.05) between all groups of treated rats regarding functional recovery. Specifically, the discrepancy among p75 siRNA and mock-transfected BMSC was statistically significant. P75 siRNA BMSC also revealed a higher level of in vivo survival compared to the mock BMSC. Conclusion: Our data suggest that genetically modified BMSC that express p75:siRNA could be a more suitable source of cells for treatment of SCI
